In this work we coupled the Ocean Modelling System - ROMS Regional Oceanic Circulation model with the MEDSLIK-II hydrocarbon dispersion model to simulate the evolution of accidental oil spills from tankers that travel near the Fernando de Noronha Archipelago in the tropical Southwest Atlantic. Six scenarios were evaluated, consisting of three spill positions on the eastern side of the Archipelago and two months (March and July). The results show that the predominance of advective forcings would tend to counteract the oil degradation processes and shorten the time window for possible mitigation actions. The worst scenario occurred in March with the plume reaching the island within 48 hours with 2.3% of the initial volume (1350 tonnes) adhering to the shore. The affected region is part of the Fernando de Noronha Marine National Park area. We propose the delimitation of a region between 3°41.9'S and 03°57'S and ~62 km perpendicular from the eastern limit of the FNA, restrictive to tanker traffic to increase the time window response in case of an oil spill.Keywords: Semi-lagrangian model, ROMS, MEDSLIK-II, Fernando de Noronha Archipelago, Oil wheathering.
Ocean dynamics initiate the structure of nutrient income driving primary producers, and these, in turn, shape the distribution of subsequent trophic levels until the whole pelagic community reflects the physicochemical structure of the ocean. Despite the importance of bottom-up structuring in pelagic ecosystems, fine-scale studies of biophysical interactions along depth are scarce and challenging. To improve our understanding of such relationships, we analyzed the vertical structure of key oceanographic variables along with the distribution of acoustic biomass from multi-frequency acoustic data (38, 70, and 120 kHz) as a reference for pelagic fauna. In addition, we took advantage of species distribution databases collected at the same time to provide further interpretation. The study was performed in the Southwestern Tropical Atlantic of northeast Brazil in spring 2015 and autumn 2017, periods representative of canonical spring and autumn conditions in terms of thermohaline structure and current dynamics. We show that chlorophyll-a, oxygen, current, and stratification are important drivers for the distribution of sound scattering biota but that their relative importance depends on the area, the depth range, and the diel cycle. Prominent sound scattering layers (SSLs) in the epipelagic layer were associated with strong stratification and subsurface chlorophyll-a maximum. In areas where chlorophyll-a maxima were deeper than the peak of stratifications, SSLs were more correlated with stratification than subsurface chlorophyll maxima. Dissolved oxygen seems to be a driver in locations where lower oxygen concentration occurs in the subsurface. Finally, our results suggest that organisms seem to avoid strong currents core. However, future works are needed to better understand the role of currents on the vertical distribution of organisms.
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